Musar para sa Levitico 19:19

“You shall not plow with an ox and an ass together” (Deuteronomy 22:21). We were warned with this not to plow - nor to tread - with two species, when they are joined with a yoke or with a rope. And the law is the same for driving them when they are joined. And [the reason] that it (only) spoke about plowing is [that] the verse mentioned the common [case]. And it is even forbidden to drive them with [one’s] voice. And it is forbidden to drive together two mules, [if] one is the daughter of a female horse and one is the daughter of a female donkey. And it is forbidden to drive a mule with [either] a horse or a donkey.

Rabbi Joshua of Sakinin in the name of Rabbi Levi in Bamidbar Rabbah 19,5, says that there are four laws in the Torah described as חק which Satan focuses on when he wants to undermine our faith. One is the law that although one must not marry a sister-in-law, the legislation of the levirate marriage contradicts that principle. Another is the legislation of כלאים, the mixing, cross-breeding or grafting of certain fabrics, animals or seeds. A third is the scapegoat that is killed on the Day of Atonement; the fourth is the legislation involving the use of the ashes of the red heifer in our portion. In connection with the prohibition of marrying a sister-in-law it is written ושמרתם את חקתי, Lev. 18,5. Nonetheless, this prohibition is set aside when one's brother had died without children. The exception to the law of לא תלבש שעטנז, in Deut. 22,11, not to wear a mixture of wool and linen, is the permission to override that principle when wearing such a mixture as part of a prayer-shawl, טלית. The exception to the principle of the ashes of the red heifer purifying a person, is that the clothing of the person or persons who actually are involved in the procedure of preparing these ashes becomes defiled even though in a state of ritual purity (19,8). The ash of the red heifer itself purifies impure clothing. There is, of course, a lot that can be queried about the whole procedure of the scapegoat. Why did Rabbi Joshua not mention other instances where the expression חק is used, without contradictory aspects to such acts of legislation?

שדך לא תזרע כלאים...בהמתך לא תרביע כלאים . The reason for this string of forbidden mixtures (19,19) is that the Creator in His wisdom saw fit to separate certain species; the account of their creation repeatedly underlines that they were created למינהו, each according to its kind, even the lowly grass (Genesis 1,12 et al). It is incumbent upon us not to upset G–d's order in the universe. We have explained that every blade of grass has a Mazal which supervises and encourages its development.